The present invention pertains to a jet engine exhaust nozzle, more particularly such a nozzle having an outlet with variable cross-sectional geometry and thrust vectoring features.
The maneuverability of high performance jet aircraft can be improved by the configuration of the exhaust nozzle of the jet engine. The modification of the cross-sectional configuration of the nozzle varies the speed of the exhaust gases to improve the adaptation of the engine to aircraft flight conditions.
It is also known to vary the orientation of the exhaust nozzle to deflect the gas jet in order to improve the maneuverability of the aircraft. Also, certain nozzles allow the reduction in height of the jet of exhaust gases passing through the nozzle so as to reduce the lateral emission of infrared rays in order to make the aircraft more difficult to detect.
The known nozzles include a plurality of articulated flaps, known as hot flaps which are in contact with the hot gas jet emanating from the aircraft engine so as to modify its cross-sectional area and configuration. Nozzles may also include a second plurality of articulated flaps, known as cold flaps, which generally form an extension of the aircraft fuselage enclosing the exhaust duct of the jet engine. In order to achieve the maximum benefits of adjustable nozzles, the movements of the hot flaps and cold flaps must be synchronized.
Some aircraft include a thrust reversing device in which the direction of the gas flow from the jet engine is altered so as to provide a reverse thrust to the aircraft. Such devices typically employ flaps or other means for blocking the pathway of the normal flow of the exhaust gases towards the rear of the aircraft so as to redirect it in a direction having a thrust component in the reverse direction.
Traditionally, exhaust nozzles have had a generally circular cross-sectional configuration in which a number, typically twelve, of primary hot flaps in direct contact with the exhaust gases from the jet engine and an equal number of cold flaps in contact with the air which flows along the fuselage of the aircraft, are controlled by actuators. The movements of the cold flaps and the hot flaps are synchronized, generally by means of interconnecting rods. Also, some nozzles utilize secondary flaps which extend between, and whose movement is controlled by, the primary hot or cold flaps. Nozzles having such configurations, in spite of their good efficiency due to the generally circular cross-sectional configuration, are particularly complex both in the structure with the overlapping of the primary and secondary flaps, and because of its controls which typically require multiple actuators.
French Patent 2 651 020 discloses a simplified exhaust nozzle having a rectangular transverse cross-section defined by four surfaces on two movable flaps and two stationary lateral flaps. The movable flaps may be oriented symmetrically during the cruising mode of operation of the aircraft and can be closed to perform a thrust reversing function. The structure of the exhaust nozzle offers limited opportunities of pivoting, especially due to the necessity of a ball and socket structure to pivotally attach the flaps to the aircraft structure. In addition, the stationary lateral flaps, or walls, generate aerodynamic disturbances both on the aircraft and in the exhaust gas flow due to leakages existing between the movable flaps and the stationary flaps. The stationary flaps also incur significant stresses due to the aerodynamic pressure exerted on them and on their supporting structure. The forces of the ejected gases also induce significant bending stresses on the movable flaps due to the location of the support bearing structure and the connection point at which the actuator is attached to the movable flap.
U.S. Pat. No. 4,878,617 discloses a converging-diverging exhaust nozzle with a variable cross-sectional area which includes thirty-six flaps, rectangular or triangular in shape, articulated between one another by piano-type hinges. Such a nozzle structure is heavy and complex, the converging section of the exhaust nozzle alone comprising fourteen flaps and four actuators. The nozzle has sections which extend into the gas stream and which introduce aerodynamic disturbances which are harmful to the efficient flow of gases through the nozzle.
In both of the aforementioned examples, the pressure exerted by the exhaust gases on the flaps is fully transmitted to the supporting structure by the control actuators, thereby requiring the supporting structure to be fabricated from material having sufficient dimensions to allow it to resist such forces.